1. Field of the Invention
The present invention relates generally to actuator arms found in hard disk drives.
2. Description of the Related Art
A hard disk drive includes a storage disk having a read/write surface and an actuator arm supporting a read/write head. In a load/unload disk drive, as the read/write head moves towards the outer diameter of the storage disk, a tab on the actuator arm slides up a ramp placed just outside the outer periphery of the storage disk. As the tab slides up the ramp, the read/write head is lifted away from the read/write surface. Thus, when the read/write head is loaded, i.e., when it is desired to read or write data, the head is loaded on to the disk, meaning that the tab slides down the ramp allowing the read/write head to move very close to the read/write surface. The head then moves across the surface of the storage disk to write data to and read data from the disk.
Conversely, when the read/write head is unloaded, the tab slides into a detent formed in the ramp such that it is xe2x80x9cparkedxe2x80x9d on the ramp. A flexible cable is attached between the actuator arm assembly and to the arm electronics module allowing data to be transmitted to and from the disk drive.
During normal unload, or emergency power shut-off, a voice coil motor (VCM) biases the actuator arm toward an outer motion-limiting crash stop. If the actuator arm moves too quickly towards the outer crash stop, it may rebound off the crash stop, preventing the tab from seating in the detent, and causing the read/write head to land back onto the disk at uncontrolled speeds that are usually higher than the designed speed. In order to prevent damage to the disk surface and read/write head, it is desirable to reduce the rebound so that the tab stays within the detent of the ramps. For this reason, the speed at which the VCM biases the actuator arm toward the outer crash stop ordinarily is constrained so that it is below a maximum threshold, e.g., four hundred and fifty millimeters per second (450 mm/s). It has been observed, however, that the bend in the flexible cable can further contribute to the speed at which the actuator arm moves toward the outer motion-limiting crash stop, hence potentially causing the arm to move too fast toward the crash stop and resulting in rebound that pushes the read/write head back onto the disk surface.
The present invention accordingly recognizes that there currently is a need to account for the velocity contribution of the flexible cable.
A method for establishing a corrected velocity of an actuator arm in a disk drive during unloading of the actuator arm includes determining a velocity contribution of a flexible cable connected to an actuator arm. Then, the velocity contribution of the flexible cable is combined with a variable velocity contribution from an actuator coil to render a corrected velocity between a predetermined minimum velocity and a predetermined maximum velocity. The corrected velocity is used to move the actuator arm during unloading of the drive, during emergency shut-down of the drive, or during loading of the drive.
In a preferred embodiment, the velocity contribution of the flexible cable is determined by moving the actuator arm to, or near, an inner motion limit. Then, an actuator coil, which is used to move the actuator arm, is deenergized and the actuator is released. As the arm moves under the influence of the flexible cable, its velocity is measured near the outer diameter of the disk to yield the velocity contribution of the flexible cable. In a preferred embodiment, the corrected velocity of the actuator is established by establishing a reduced power to the actuator coil. It is possible that the contribution from the flex cable could be in the opposite direction, such that, the bias moves the actuator towards the inner diameter of the disk. In this case, the power to the actuator coil must be increased. Preferably, the method of the present invention is performed during testing of the disk drive before it is shipped to a user, but it may also be performed periodically over the life of the disk drive.
In another aspect of the present invention, a disk drive includes a disk and an actuator arm. The disk drive also includes a read/write head that is supported by the actuator arm. A flexible cable is attached to the actuator arm and an actuator coil is also connected to the actuator arm. Accordingly, the actuator coil is used to drive the actuator arm. In this aspect of the present invention, the disk drive includes a control circuit that includes means for establishing a corrected velocity of the actuator arm to be used during unloading of the disk drive.
In yet another aspect of the present invention, a method for measuring a velocity contribution of a flexible cable in a disk drive includes moving an actuator arm to a motion limit, e.g., an inner motion limit or an outer motion limit. Then, an actuator coil, which is connected to the actuator arm, is deenergized and the actuator arm is released. As the actuator arm moves under the influence of the flexible cable, a parameter representative of actuator arm motion is measured. A corrected velocity of the actuator arm is established based on the parameter.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: